1. Field of the Invention
The present invention relates to a key switch assembly for a computer keyboard, more particularly to a key switch assembly which has a relatively simple and stable structure with a reduced thickness.
2. Description of the Related Art
FIG. 1 illustrates a conventional key switch assembly which includes a base board 1, a membrane circuit plate 2 disposed on the base board 1, a resilient layer 3 provided on the membrane circuit plate 2, a bridge-device support plate 4 disposed on the resilient layer 3, a key cap 6, a bridge device 5 provided between the support plate 4 and the key cap 6, and a resilient biasing member 3a extending from the resilient layer 3 and through the support plate 4 and the bridge device 5 to bias the key cap 6 upwardly. The support plate 4 has pivot retainer plates 4b for retaining pivotally the lower end of a front section of the bridge device 5, and slide retainer plates 4a for retaining slidably the lower end of a rear section of the bridge device 5. The key cap 6 has a bottom side provided with a pivot retainer unit 6b for retaining pivotally the upper end of the front section of the bridge device 5, and a slide retainer unit 6a for retaining slidably the upper end of the rear section of the bridge device 5.
The above-described key switch assembly can be operated by depressing the key cap 6 to cause the membrane circuit plate 2 to create an electrical signal, and by releasing the key cap 6 to allow the key cap 6 to be biased upwardly by the biasing member 3a. In recent years, computer keyboards tend to be made thinner to reduce the size of computers, especially in portable computer applications. It is noted that the aforementioned key switch assembly has a relatively large thickness which cannot be significantly reduced since the bridge device 5 is provided between the key cap 6 and the support plate 4. The key switch assembly of FIG. 1 is thus not suitable for use in a portable computer.
FIG. 2 illustrates another conventional key switch assembly which also includes a base board 7, a membrane circuit plate 7c, a resilient layer 7d, a scissors-type bridge device 8, a key cap 9, and an upright biasing member 9c provided on the resilient layer 7d. The base board 7 has two pairs of pivot lobes 7a, 7b which extend upwardly through the membrane circuit plate 7c and the resilient layer 7d. The pivot lobes 7a have inclined, elongated pivot holes 7a' formed therein. The scissors-type bridge device 8 has lower ends mounted pivotally to the pivot lobes 7a, 7b, and upper ends mounted pivotally to elongated slots 9a and pivot grooves 9b formed on a bottom side of the key cap 9.
Although the key switch assembly of FIG. 2 has a reduced thickness as compared to the conventional key switch assembly of FIG. 1 in view of the mounting of the bridge device 8 between the base board 7 and the key cap 9, the key switch assembly of FIG. 2 still suffers from the following disadvantages:
1) The inclined, elongated pivot holes 7a' can result in deformation and unstable movement of the bridge device 8 when the key cap 9 is depressed.
2) During assembly, pin protrusions provided on the lower ends of the bridge device 8 must be forced inwardly at first so that they can be mounted within the pivot lobes 7a, 7b. The key switch assembly is thus difficult to assemble and might be damaged during assembly of the same.
3) Since no engagement means is provided between the key cap 9 and the biasing member 9c, improper operation of the key switch assembly can result when the key cap 9 is depressed.
In addition, in a typical notebook computer, electrical connectors of the membrane circuit plate must be bent and disposed between the membrane circuit plate and the base board due to insufficient space within the notebook computer. As such, an opening might be formed between the base board and the membrane circuit plate. Dust can easily enter into the opening between the base board and the membrane circuit plate during assembly and transport of the notebook computer, thereby affecting the conductivity of the membrane circuit plate.